The present invention relates generally to linear actuators, and in particular to a linear voice coil actuator with a latching feature.
An example of a typical linear voice coil actuator is depicted in a one-half-cross section in FIG. 1, and consists of a field assembly 10 and a coil assembly 20. The field assembly 10 is comprised of an axially magnetized cylindrical magnet 12, soft magnetic pole piece 14 and soft magnetic housing 16. The coil assembly 20 consists of a coil 22, located in the circular cavity 23 of the coil base 24. The coil assembly 20, when de-energized, does not have a preferred position to go to. When such a position is required by the system operation, some kind of latching feature has to be provided.
The linear voice coil actuator of the subject application provides such a latching feature, and includes a coil assembly, a field assembly, and a magnetic structure positioned in the coil assembly. The coil assembly has a coil base and a coil located in a cavity in the coil base. The field assembly preferably has an axially magnetized cylindrical magnet, a soft magnetic pole piece, and a soft magnetic housing having sides which define a cavity. The coil of the coil assembly is positioned in a gap defined between interior surfaces of the sides of the magnetic housing and the soft magnetic pole piece and magnet. Preferably the magnetic structure is a magnetic plate positioned coaxially with the axis of magnetization of the magnet and having a diameter or a thickness that is selected to set a latching force between the plate and the magnet when the coil is not energized. Preferably a stop limits the position of the magnetic structure with respect to the field assembly when the coil of the coil assembly is not energized.
It is therefore an object of the present invention to provide a linear actuator having a latching feature.
It is another object of the present invention to provide a linear actuator in which a latching feature is provided by a magnetic structure positioned in the coil assembly of the actuator.
It is a further object of the present invention to provide a linear actuator in which a latching feature is provided by a magnetic plate positioned in a coil assembly wherein the thickness or diameter of the magnetic plate is selected to define a latching force between the coil assembly and a field assembly of the actuator when the coil assembly is not energized.
These and other features and advantages of the present invention will be more readily understood upon consideration of the following detailed description and accompanying drawings.